Non-alloyed Al ohmic contact to GaAs for GaAs/Si interconnect compatibility

An alternative to Au-based GaAs ohmic contacts, a nonalloyed aluminium contact that is ohmic because of the presence of delta -doping at the surface of the GaAs, is presented. The contact is entirely grown by molecular beam epitaxy (MBE), with the aluminum deposited in the MBE chamber immediately after growth. A contact resistance of 2.5*10/sup -6/ Omega -cm/sup 2/ is obtained, which is several times better than previous nonalloyed ohmic contacts to GaAs. This is attributed to the deposition of the metal before it is exposed to air, so that no oxide forms at the GaAs surface. Another reason for the improvement is that the aluminum wets the GaAs surface and forms an epitaxial relationship with the GaAs, so that it is crystalline. Since it is aluminum, the contact is compatible with aluminum-based silicon IC interconnection technology, allowing GaAs-Si integration without the 'purple plague' associated with Au-Al contacts.<
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